Monday, December 31, 2012

Grab Bag: Raspberry Pi Case and App Store

I was ordering some electronic parts from Jameco recently and I notice they now carry an inexpensive Raspberry Pi case, so I ordered one. The case is made by Bud Industries. It is a simple design with only two (identical) plastic pieces that go together. It's a little big, but has the benefit of allowing lots of ventilation and it will probably have room for some of the available expansion boards or a ribbon cable connector to the GPIO pins.

Raspberry Pi Case
Recently I was digging through my junk box looking for a specific chip and realized I don't have very many TTL chips. I like electronics grab bags, and Jameco sells a number of different ones, so I also picked up their 100 Piece TTL Semiconductor Grab Bag. I just started sorting them but it looks like I got quite a good assortment of devices. They say it can contain surface mount parts as well as through hole but my grab bag only included DIP packages, which is great.

100 TTL Chips
The Raspberry Pi foundation recently opened an application store, for both paid and free apps. So I ported a small text adventure game that I wrote in C, originally for my Apple 1 replica, and packaged it for the Raspberry Pi store. It is a free download and you can get it from here.  I think the game is quite challenging and I encourage you to try it out if you have a Raspberry Pi. I'm also working on a graphical version that will use the Qt toolkit.

Friday, December 28, 2012

SB-310 Heathkit Catalog Listing

Here are scans of the listing for the SB-310 shortwave receiver from the 1971 US Heathkit catalogue. It was sold from 1967 to 1972 when it was replaced by the solid state SB-313. It originally came with a copy of the World Radio TV handbook shown here. The ashtray and pipe were not included :-)

SB-310 Receiver Gets A Speaker

I was able to get a matching SB-600 speaker on eBay for my SB-310 shortwave receiver. It has some paint chips but is not too bad looking overall. Probably thousands of these speakers were sold by Heathkit for the matching SB and HW series radios from 1966 through 1975, retailing for US$17.95 They tend to go for quite a high price on eBay. I got mine for a good price - probably because the seller listed it as an "SP-600" rather than an "SB-600" so many potential buyers may have missed it in searches.

SB-310 and SB-600 Speaker
The restoration of this radio only consisted of putting on a new line cord, cleaning it, and touching up the alignment. I made some rubber feet using rubber stoppers cut to size and drilled for a screw. I initially thought it was missing the 100 KHz crystal but it was installed in the LSB crystal socket (which is normally empty) by mistake.
Another View of the SB-310 Receiver
It is a good performer, picking up lots of shortwave stations in the evenings. The dial is linear and very accurate.

Repaired Function Switch With Microswitch
I was also able to fix the main issue with my SB-310, the broken power switch. It is a combined rotary wafer switch and power switch on the FUNCTION switch. Getting a new switch is almost impossible. I was able to rig up a micro switch in such a way as to be controlled by the rotor of the function switch. Provided that the Gorrilla glue holding the switch stays in place, it should do the job.

Tuesday, December 18, 2012

Raspberry Pi Radiation Monitor

Some time ago built this Geiger counter kit. Details are in this Youtube video. I originally hooked it up via a serial port to a Linux desktop system running an Apache web server and wrote a simple shell script that displayed the current radiation level. Recently I moved it over to a Raspberry Pi.

The serial port uses the AdaFruit FTDI friend to convert the 3.3V level serial port on the Geiger counter to a USB serial device.

My son recently wrote some Python code to generate a nicer looking web page that includes a graph.
It uses the RGraph library.

I then made a little C program that reads the radiation data from the serial port, and writes it out in CSV format so it can be easily parsed by the Python code that generates the graphs. A cron job updates the web page every hour with the latest data.

Here is a picture of the hardware setup using a Raspberry Pi as the attached computer which is running the Apache web server:

And here is a closer shot of the Geiger counter:

Here is an image of a typical web page:

And here are some items that I use for testing the Geiger counter that are slightly radioactive: a couple of buttons made from glass that is coloured with Uranium:

If the system is active and I am not otherwise using the Raspberry Pi for something else, you can see the graph at this URL.

Sunday, December 16, 2012

A Small Collection of Digital Multimeters

I realized I have a small collection of DMMs (Digital MultiMeters) around that I have collected over the years. At one time most of these have been my primary meter for electronic work.

Left to right, we have a low cost non-autoranging model branded for Canadian Tire, followed by a newer auto-range but still low cost Canadian Tire branded model.

Then an early 1980s vintage Heathkit unit I bought at a garage sale, followed by a good quality Extech unit which is my current meter of choice, and finally a very small and low cost DMM I bought earlier this year that is handy to have around the bench to make quick measurements.

Sunday, December 2, 2012

Heathkit SB-310 Shortwave Receiver

I recently purchased a Heathkit SB-310 shortwave receiver on Ebay and am restoring it. The SB-310 was Heathkit's top of the line shortwave receiver, based on the SB-300 Amateur Radio receiver.

It is an all tube receiver that was sold as a kit from  1967 to 1972 retailing at US$267.95. It covers nine shortwave bands which over most of the shortwave, amateur radio, and CB radio bands.

It has a very accurate and linear dial which used the heathkit LMO (Linear Master Oscillator) which was pre-assembled and aligned.

I post more details here later on the work to restore it, which was not much as the unit I purchased was working and very clean when I received it.